In recent years, in portable devices such as mobile phones, mobile information terminals, digital cameras, and laptop type personal computers, the respective original functions such as a telephony calling function, schedule management, and document creation are becoming more multifunctional and exceeding their functional boundaries. For example, on a mobile phone, in addition to email transmitting/receiving functions, there have been added various types of functions such as a website viewing function, a gaming function, and a television watching function.
Under these circumstances, mobile terminals have become deeply rooted into our lives, and the level of the need for always having them is becoming higher as a result. For example, use of mobile terminals in outdoor areas, under rainy weather conditions, or during outdoor activities may be assumed. In order to ensure reliability under these types of conditions, there is a strong demand for an environment-adapting waterproofing property to be provided in mobile terminals.
Consequently, various types of waterproof structures have been proposed. In general, it is necessary to seal out liquid droplets in order to ensure waterproofness. Accordingly, there is widely known a packing structure in which a rubber based material such an O-ring is compressed and deformed, and the repulsive force thereof is used to bring it into close contact with a casing, to thereby ensure sealing. A packing structure uses repulsive force which is exerted when being compressed, and therefore, a compressing load is required. Various schemes have been proposed in order to reduce this load.
For example, in a portable information processing device disclosed in Patent Document 1, between an information input means on an information display means serving as a casing, and an external casing, there is provided a flexible TP cushion including a protruding waterproof rib and a concave waterproof groove. In a waterproof structure realized by means of the packing disclosed in Patent Document 2, between casing members forming a casing, there is provided a packing including an elastic ring. In a waterproof structure disclosed in Patent Document 3, a packing is provided on an outer periphery part between a front casing and a rear casing forming a casing. In a waterproof structure disclosed in Patent Document 4, no packing is used on the facing surface of a member which forms a casing, and waterproofness is ensured by coating it with a water repellent film.